Abstract
An optical modulator for switching an optical signal of wavelength λ from one waveguide-electrode to another requires that both waveguide-electrodes be made of an electrically conducting material. Also, a non-conducting cross-coupling material fills a slot along a length L between the waveguide-electrodes. Importantly, cross-coupling material in the slot provides a separation distance x.sub.c between the waveguide-electrodes that is less than 0.35 microns. When a switching voltage V.sub.π is selectively applied to the waveguide-electrodes, a strong uniform electric field E is created within the cross-coupling material. Thus, E modulates the cross-coupling length of the optical signal by an increment ±Δ each time it passes back and forth through the cross-coupling material along the length L. Thus, after an N number of cross-coupling length cycles along the length L, when NΔ equals one cross-coupling length, the optical signal is switched from one waveguide-electrode to the other.
Claims
1. An optical modulator for switching an optical signal of wavelength λ between two waveguides, which comprises: a first waveguide-electrode made of an electrically conductive material and having an input port and an output port with a length L therebetween; a second waveguide-electrode made of an electrically conductive material and having an input port and an output port, wherein the first waveguide-electrode and the second waveguide-electrode are oriented in a side-by-side alignment along the length L; a non-conducting cross-coupling material positioned between the first waveguide-electrode and the second waveguide-electrode along the length L to establish a slot having a separation distance x.sub.c therebetween, wherein x.sub.c is less than 0.35 microns to establish a cross-coupling length L.sub.c for the optical signal during transit through the cross-coupling material from one waveguide-electrode to the other, wherein L.sub.c approaches the wavelength λ; and a voltage source electrically connected to the first waveguide-electrode and to the second waveguide-electrode to selectively apply a switching voltage V.sub.π therebetween for creating a strong, uniform electric field E confined within the cross-coupling material along the length L, to modulate the cross-coupling length L.sub.c by an increment Δ, to establish a modulated cross-coupling length L.sub.c′(L′=L.sub.c±Δ) for switching the optical signal from one waveguide-electrode to the other, wherein switching occurs after an N number of cross-coupling length cycles of the optical signal along the length L in the waveguide-electrodes, when L.sub.c′=NΔ, and L=NL.sub.c=(N±1)L.sub.c′.
2. The optical modulator recited in claim 1 wherein L is in a range between 0.5 mm and 5 mm.
3. The optical modulator recited in claim 1 wherein L is in a range between 0.5 μm and 5 μm.
4. The optical modulator recited in claim 1 wherein no switching occurs when the voltage source applies a voltage V.sub.base, and causes switching when an applied voltage from the voltage source equals V.sub.base+V.sub.π.
5. The optical modulator recited in claim 4 wherein V.sub.base=0.
6. The optical modulator recited in claim 1 wherein the first waveguide-electrode and the second waveguide-electrode are made of a conducting semiconductor material.
7. The optical modulator recited in claim 1 wherein the non-conducting cross-coupling material is a polymer and has an index of refraction n, wherein n is a function of an electro-optical index modulation coefficient r modulated by V.sub.π, with r greater than 20 pm/V.
8. The optical modulator recited in claim 1 wherein the cross-coupling material in the slot establishes an optical slot confinement factor Γ, wherein the confinement factor Γ is greater than 0.15 when x.sub.c is less than 0.35 μm, to create a modulated cross-coupling length L.sub.c′ less than 2λ under the influence of V.sub.π (Γ>0.15, when x.sub.c<0.35 μm, to achieve L.sub.c′<2λ).
9. The optical modulator recited in claim 1 wherein the length L of the slot is determined relative to the modulation increment Δ created by the switching voltage V.sub.π to establish a relationship wherein L=NL.sub.c=(N±1)L.sub.c′.
10. A method for manufacturing an optical modulator for switching an optical signal between two waveguides, wherein the optical signal has a wavelength λ and follows a wave path through the optical modulator, the method comprising the steps of: providing a non-conducting cross-coupling material, a first waveguide-electrode and a second waveguide-electrode, wherein each waveguide-electrode is made of an electrically conductive material and has an input port and an output port with a length L therebetween; orienting the first waveguide-electrode to the second waveguide-electrode in a side-by-side alignment to create a slot therebetween along the length L, wherein the slot has a separation distance x.sub.c between the first and second waveguide-electrodes, and x.sub.c is less than 0.35 microns; and filling the slot between the first waveguide-electrode and the second waveguide-electrode with the non-conducting cross-coupling material along the length L to establish an optical slot confinement factor Γ in the slot wherein, when a switching voltage V.sub.π is applied between the first and second waveguide-electrodes, the confinement factor Γ is greater than 0.15 to create a cross-coupling length L.sub.c less than 2λ for the optical signal during transit through the cross-coupling material from one waveguide-electrode to the other (Γ>0.15, when x.sub.c<0.35 μm, to achieve L.sub.c′<2λ).
11. The method recited in claim 10 further comprising the step of connecting a voltage source to the first waveguide-electrode and to the second waveguide-electrode to selectively apply the switching voltage V.sub.π therebetween for creating a strong, uniform electric field E confined within the cross-coupling material along the length L, to modulate the cross-coupling length L.sub.c of the optical signal by an increment Δ and establish a modulated cross-coupling length L.sub.c′(L.sub.c′=L.sub.c±Δ), wherein after an N number of cross-coupling length cycles of the optical signal along the length L in the waveguide-electrodes, when L=NL.sub.c=NL.sub.c′±NΔ and L.sub.c′=NΔ, the optical signal is switched from one waveguide-electrode to the other.
12. The method recited in claim 11 wherein the length L of the slot is determined relative to the modulation increment Δ created by the switching voltage V.sub.π to establish a relationship wherein L=NL.sub.c=(N±1)L.sub.c′.
13. The method recited in claim 12 wherein L.sub.c is in a range between 0.5 μm and 5 μm.
14. The method recited in claim 12 wherein L is in a range between 0.5 mm and 5 mm.
15. A method for manufacturing an optical modulator for switching an optical signal between two waveguides, wherein the optical signal has a wavelength λ and follows a wave path through the optical modulator, the method comprising the steps of: providing a non-conducting cross-coupling material, a first waveguide-electrode and a second waveguide-electrode, wherein each waveguide-electrode is made of an electrically conductive material and has an input port and an output port with a length L therebetween; orienting the first waveguide-electrode parallel to the second waveguide-electrode in a side-by-side alignment to create a slot therebetween along the length L, wherein the slot has a separation distance x.sub.c between the first and second waveguide-electrodes, and x.sub.c is less than 0.35 microns; and filling the slot between the first waveguide-electrode and the second waveguide-electrode with the non-conducting cross-coupling material along the length L, wherein the length L is established for a requirement that the wave path of the optical signal be changed by a length less than 2λ during transit of the optical signal along the length L.
16. The method recited in claim 15 wherein the orienting step establishes an optical slot confinement factor Γ in the slot wherein, when a switching voltage V.sub.π is applied between the first and second waveguide-electrodes, the confinement factor Γ is greater than 0.15 to create a cross-coupling length L.sub.c less than 2λ for the optical signal during transit through the cross-coupling material from one waveguide-electrode to the other (Γ>0.15, when x.sub.c<0.35 μm, to achieve L.sub.c′<2λ).
17. The method recited in claim 15 further comprising the step of connecting a voltage source to the first waveguide-electrode and to the second waveguide-electrode to selectively apply the switching voltage V.sub.π therebetween for creating a strong, uniform electric field E confined within the cross-coupling material along the length L, to modulate the unmodulated cross-coupling length L.sub.c of the optical signal by an increment Δ and establish a modulated cross-coupling length L.sub.c′(L.sub.c′=L.sub.c±Δ), wherein after an N number of cross-coupling length π cycles of the optical signal along the length L in the waveguide-electrodes, when L=NL.sub.c=NL.sub.c′±NΔ and L.sub.c′=NΔ, the optical signal is switched from one waveguide-electrode to the other.
18. The method recited in claim 15 wherein L.sub.c is in a range between 0.5 μm and 5 μm.
19. The method recited in claim 15 wherein L is in a range between 0.5 mm and 5 mm.
20. The method recited in claim 15 wherein the first and second waveguides are made of a conducting semiconductor material.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
[0046] FIG. 1 is a perspective-schematic view of a system for transmitting optical signals, which includes an electro-optically coupled switch in accordance with the present invention;
[0047] FIG. 2 is a cross-section view of an embodiment of the electro-optically coupled switch for the present invention as seen along the line 2-2 in FIG. 1;
[0048] FIG. 3 is a cross-section view of an exemplary switch in accordance with the present invention, as seen along the line 3-3 in FIG. 1, showing the switch/modulation functionality of the present invention;
[0049] FIG. 4 is a cross-section view of another embodiment of the electro-optically coupled switch for the present invention as seen along the line 4-4 in FIG. 1;
[0050] FIG. 5 is a cross-section view of still another embodiment of the electro-optically coupled switch for the present invention as seen along the line 5-5 in FIG. 1;
[0051] FIG. 6 is a perspective view of a work piece used for a manufacture of the electro-optically coupled switch of the present invention;
[0052] FIG. 7A is a cross-section of the work piece as seen along the line 7-7 in FIG. 6, with the work piece in an intermediate configuration during a manufacturing process;
[0053] FIG. 7B is a view of the work piece as seen in FIG. 7A after manufacture and ready for subsequent assembly in an operational switch;
[0054] FIG. 8 is a sequence of evolving cross-sections of the work piece as seen in FIGS. 7A and 7B, with the sequence showing eight different manufacturing steps, respectively numbered (1) through (8), in a manufacture of the present invention;
[0055] FIG. 9A is a top plan view of a first mask for use in the manufacture of the present invention;
[0056] FIG. 9B is a top plan view of a second mask for use in the manufacture of the present invention;
[0057] FIG. 9C is a top plan view of a third mask for use in the manufacture of the present invention;
[0058] FIG. 10 shows representative modulated and unmodulated wave paths for an optical signal with comparative changes in the respective cross-coupling lengths of the optical signal during one cycle in accordance with the present invention;
[0059] FIG. 11A is a cross-section view of the waveguides for an optical modulator of the present invention as seen in FIG. 3 showing the progress of an optical signal along a length L of the waveguides when the cross-coupling switching voltage V.sub.π equals zero or a base value V.sub.base, and no switching action is in progress;
[0060] FIG. 11B is the cross-section view of the optical modulator shown in FIG. 11A when a switching voltage V.sub.π is applied during a switching operation in accordance with the present invention; and
[0061] FIG. 12 is a cross-section view of the waveguides as seen along the line 12-12 in FIG. 11A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] Referring initially to FIG. 1, an electro-optically coupled switch in accordance with the present invention is shown and is generally designated 10. As shown, the switch 10 includes an enclosure 12 for holding and protecting the electro-optic components of the switch 10. Also, an access connector 14 is provided for connecting the electro-optic components (not shown in FIG. 1) with an external voltage source 16. A queue control 18 and a routing control 20 are incorporated with the voltage source 16 to respectively provide for the sequencing, routing and modulation of optical signals, λ, as they pass through the electro-optically coupled switch 10.
[0063] Still referring to FIG. 1, it will be seen that the enclosure 12 includes an input port 22 for optically connecting an optical waveguide 24 with the switch 10. Similarly, an input port 26 is provided by the enclosure 12 for optically connecting an optical waveguide 28 with the switch 10. It is to be appreciated that the optical waveguides 30 and 32 will have similar connections with the enclosure 12.
[0064] In FIG. 2 the internal, electro-optic components for a preferred embodiment of the switch 10 are shown. There it will be seen that the switch 10 includes a waveguide 34 and a waveguide 36 that are respectively protected by a cladding 38 and a cladding 40. In more detail, each waveguide 34 and 36 has a width, W, and a length, L, and they are vertically aligned in parallel with each other. Further, as shown, the switch 10 includes a metal connector 42 (e.g. +V) and a metal connector 44 (e.g. −V) which are respectively connected with a transparent electrical contact 46 and a transparent electrical contact 48. Further, a cross-coupling material 50 is positioned between the transparent electrical contacts 46 and 48. In accordance with the present invention, the transparent electrical contacts 46 and 48 are in direct contact with the cross-coupling material 50, and are everywhere separated from each other by a distance, d. Further, the transparent electrical contacts 46 and 48 are positioned opposite each other from the cross-coupling material 50. And, they are each positioned between the cross-coupling material 50 and a respective waveguide 34 and 36. Additionally, a filler material 52 is provided to electrically confine the cross-coupling material 50 between the transparent electrical contacts 46 and 48.
[0065] Within the combination of components for the switch 10 shown in FIG. 2, the differences in the refractive index of the various materials used are important. In detail, the refractive index of waveguide 34 (a first waveguide), n.sub.wg1, will be equal to, or nearly equal to, the refractive index of waveguide 36 (a second waveguide), n.sub.wg2. For purposes of the present invention, the refractive indexes of the waveguides 34 and 36 will be the same, or nearly the same, n.sub.wg1≈n.sub.wg2. Importantly, however, the refractive index of the cross-coupling material 50, n.sub.c, (also sometimes noted herein as n.sub.eo) needs to be much greater than the respective indexes n.sub.wg1 and n.sub.wg2 of the first and second waveguides 34 and 36 (i.e. n.sub.wg1<<n.sub.c>>n.sub.wg2). As noted above, this arrangement is made to achieve strong waveguide cross-coupling, good optical confinement in the cross-coupling material, and efficient electro-optic modulation, with a proper waveguide separation distance, d. For example, n.sub.c=1.7, n.sub.wg=1.57, and d=0.5 μm. Also, the refractive index of the filler material 52, n.sub.f, needs to be smaller than all of the others (i.e. n.sub.c>>n.sub.wg(1 and 2)>n.sub.f, and n.sub.wg1≈n.sub.wg2).
[0066] As shown, the metal connector 42 and the metal connector 44 are separately connected with the voltage source 16. Thus, a +V can be provided to the metal connector 42 by the voltage source 16, and a −V can be provided to the metal connector 44. The result is that a switching voltage, ΔV.sub.π, can be applied through the cross-coupling material 50 that will change its refractive index, n.sub.c. As envisioned for the present invention, the cross-coupling material 50 may be a polymer, when the waveguides 34 and 36 are also polymers, or when the waveguides 34 and 36 are made of a SiON/silica material.
[0067] An operation of the switch 10 will be best appreciated with reference to FIG. 3. There it will be seen that, depending on the influence of the switching voltage, V.sub.π, an optical signal, λ, can be directed either onto a pathway 54 (solid arrows) or a pathway 56 (dashed arrows). The consequence of this is that, the switching voltage, V.sub.π, can be used to guide an optical signal, λ, which enters the switch 10 through the input port 22 to exit the switch 10 from either the output port 58 of waveguide 36 or the output port 60 of waveguide 34.
[0068] With the above in mind, and by returning to FIG. 1, it will be appreciated that the routing control 20 can influence the voltage source 16 to selectively establish the switching voltage, V.sub.π, and thereby generate the electrical field, E. Importantly, the electrical field, E, when generated, is uniform with the flux lines of the field oriented substantially perpendicular to the length, L, of the waveguides 34 and 36. As mentioned above, the purpose here is to influence the transit of an optical signal, λ, through the switch 10.
[0069] For an exemplary operation of the switch 10, refer back to FIG. 1. In this example, consider an optical signal, λ.sub.in-a, as input from optical waveguide 24, into the waveguide 36 via input port 22. Also consider an optical signal, λ′.sub.in-b, as input from optical waveguide 28, into the waveguide 34 via input port 26. For purposes of this example, subscript “a” pertains to waveguide 36, while subscript “b” pertains to waveguide 34.
[0070] With cross-reference between FIG. 1 and FIG. 3, and first considering only the optical signal, λ, it is to be appreciated that with no switching voltage, V.sub.π, there is no electric field, E, through the cross-coupling material 50. Accordingly, optical signal, λ.sub.in-a, in optical waveguide 24 will enter switch 10 via input port 22, transit switch 10 on pathway 54, and exit from switch 10 via the output port 58 (FIG. 3) and into the optical waveguide 30 as optical signal, λ.sub.out-a. On the other hand, with a switching voltage, V.sub.π, imposed on the cross-coupling material 50, an electric field, E, is generated through the cross-coupling material 50 to change the refractive index, n.sub.c (n.sub.eo), of the cross-coupling material 50. In this case, the optical signal, λ.sub.in-a, will transit switch 10 on pathway 56, and exit from switch 10 via the output port 60 (FIG. 3), and into the optical waveguide 32 as optical signal, λ.sub.out-b.
[0071] Similarly, when considering the optical signal, λ′, it is to be appreciated that with no switching voltage, V.sub.π, optical signal, λ′.sub.in-b, will enter switch 10 from optical waveguide 28 via input port 26. Optical signal, λ′.sub.in-b, will then transit switch 10 and exit via the output port 60 (FIG. 3) and into the optical waveguide 32 as optical signal, λ′.sub.out-b. With a switching voltage, V.sub.π, imposed on the cross-coupling material 50, however, the optical signal, λ′.sub.in-b, will transit switch 10 to exit from switch 10 via the output port 58 (FIG. 3), and into the optical waveguide 30 as optical signal λ′.sub.out-a.
[0072] Still referring to FIG. 1 it is to be appreciated that the switch 10 can be used either as a switch or as a modulator. Further, it will be appreciated that the queue control 18 can be used as a gate to provide for alternating or sequential access of the optical signals, λ and λ′, to the switch 10. As will be appreciated by the skilled artisan, when switch 10 is used as a modulator, only one continuous wave (CW) light input port 22 and one optical output port (e.g. output port 58, FIG. 3) are required.
[0073] FIG. 4 shows an alternate embodiment for the present invention wherein the waveguide 34 and the waveguide 36 are each made of a same, lightly-doped, electrically-conductive material. As shown, the waveguides 34 and 36 are individually positioned in contact with the voltage source 16. For one alternate embodiment of the present invention, both the waveguide 34 and the waveguide 36 are N doped. Accordingly, the means for imposing the switching voltage, V.sub.π, includes an N.sup.+ doped layer 62 that is positioned in electrical contact between the N doped waveguide 34 and the metal connector 44. Similarly, an N.sup.+ doped layer 64 is positioned in electrical contact between the N doped waveguide 36 and the metal connector 42. Preferably, for this alternate embodiment of the present invention, the cross-coupling material 50 is a polymer.
[0074] FIG. 5 shows another alternate embodiment of the present invention wherein the waveguide 34 is P doped and the waveguide 36 is N doped. In this case, the means for imposing V.sub.π includes a P.sup.+ doped layer 66 positioned in electrical contact between the P doped waveguide 34 and the metal connector 44. Also included is an N.sup.+ doped layer 68 which is positioned in electrical contact between the N doped waveguide 36 and the metal connector 42. In this case, the cross-coupling material 50 can be either a PIN planar-diode-structure semiconductor, or a PIN multiple-quantum-well semiconductor.
[0075] Referring now to FIG. 6, a method for manufacturing an electro-optically coupled switch in accordance with the present invention is disclosed. In FIG. 6 it will be appreciated that the method first requires providing a base member that has been generally designated 80. As shown, the base member 80 includes a layer 82 of a semiconductor material. Also, the base member 80 includes a layer 84 of an insulator material that is positioned between the semiconductor layer 82 and a substrate 86 that is also made of a semiconductor material. For purposes of the present invention, the semiconductor material that is used for the layer 82 may be of any type well known in the pertinent art, such as silicon, or compound semiconductors such as InP, GaAs, GaN, or a quantum well composition of various compound semiconductors.
[0076] When constructed, the base member 80 will have a length L, a width W.sub.s and a thickness T. The base member 80 will also have opposite edges 88a and 88b which straddle the central plane 90 that is defined by the base member 80.
[0077] As an overview of the methodology for the present invention, FIG. 7A shows that the semiconductor layer 82 is to be reconfigured to form a slot 92 which is positioned along the central plane 90 between opposed waveguides 94a and 94b. Note: the depth of the slot 92 extends through the semiconductor layer 82 to expose the layer 84 of insulator material. Still referring to FIG. 7A it will be appreciated that the slot 92 will have a width x.sub.c along the length L of the slot 92, and that the waveguides 94a and 94b each have an operational width x.sub.w adjacent the slot 92, as well as an extension of width x.sub.e that extends from the waveguides 94a and 94b toward the edges 88a and 88b of the base member 80.
[0078] FIG. 7B shows that the semiconductor layer 82 will be further reconfigured to form contact pads 96a and 96b at the edges 88a and 88b of the base member 80. Additionally, metal electrodes 98a and 98b are then to be positioned in electrical contact with the respective contact pads 96a and 96b. Further, FIG. 7B shows that the slot 92 is filled with a cross-coupling material 100. For purposes of the present invention, the cross-coupling material 100 can be of any type material known in the pertinent art for the specified purposes of the present invention. Preferably, the cross-coupling material 100 will be a polymer. With the above overview in mind, the methodology of the present invention is best appreciated with reference to FIG. 8 and FIGS. 9A, 9B and 9C.
[0079] FIG. 8 shows that the method for manufacturing an electro-optically coupled switch is essentially an eight step process. In FIG. 8, these steps are designated sequentially as (1), (2), (3) . . . (8). To begin, as shown in FIG. 8(1), a base member 80 is constructed as disclosed above. Then, a first mask 102 is positioned on the layer 82 of semiconductor material and it is aligned on the layer 82 relative to the central plane 90 substantially as shown in FIG. 9A. As best seen in FIG. 9A, the first mask 102 is formed with a central cutout 104 and a pair of side cutouts 106a and 106b. Between the central cutout 104 and the side cutouts 106a and 106b are two parallel strips 108a and 108b that are separated from each other by the distance x.sub.c. With the first mask 102 in position on the layer 82, FIG. 8(2) shows that, in a first etch, the semiconductor material in the layer 82 is etched to a depth of d.sub.1. The result here is to create a reconfigured layer 82′ that is formed with the slot 92.
[0080] FIG. 8(3) shows that after the first etch, a second mask 110 is positioned over the first mask 102. FIG. 9B shows that this second mask 110 is formed with only a central cutout 104′. For purposes of the present invention, this central cutout 104′ can be formed with a width W.sub.c where x.sub.c<W.sub.c<x.sub.c+2x.sub.w. In any event, the second mask 110 is intended to mask the entire layer 82′ with the exception of the slot 92. Accordingly, in a second etch, with the second mask 110 in place, the layer 82′ of semiconductor material can be further reconfigured. Specifically, as shown in FIG. 8(3), semiconductor material in the slot 92 can be removed through the depth d.sub.2 to expose insulator material in the layer 84. The second mask 110 and the first mask 102 can then be removed.
[0081] In the next sequential step, FIG. 8(4) shows that a third mask 112 is positioned over the layer 82 of semiconductor material to cover the slot 92 and portions of the waveguides 94a and 94b. For the present invention, the third mask 112 is essentially a solid panel 114 (See FIG. 9C). This effectively exposes the edge segments 116a and 116b shown in FIG. 8(4). Thus, semiconductor material in the edge segments 116a and 116b of layer 82 can be heavily doped in this process. As shown in FIG. 8(5), after the doping of edge segments 116a and 116b, the respective contact pads 96a and 96b can be formed. As noted above, the contact pads 96a and 96b are preferably formed by N.sup.+ doped semiconductor material.
[0082] With the above in mind, it follows as shown in FIG. 8(6) that metal electrodes 98a and 98b can be positioned on respective contact pads 96a and 96b. FIG. 8(7) then indicates that the next step in the methodology is to fill the slot 92 with a cross-coupling material 100, such as an electro-optical polymer. A final step, which is appreciated with reference to FIG. 8(8), is that the cross-coupling material 100 (i.e. electro-optical polymer) can be poled in the slot 92 to optimize its electro-magnetic coefficient for cross-coupling optical signals as they pass through the waveguides 94a and 94b.
[0083] In another aspect of the present invention, the modulation for switching an optical signal from one waveguide to another is accomplished by electro-optically changing the cross-coupling length of path 202 for the optical signal. With reference to FIG. 10, several considerations for the switching function provided by this aspect of the invention are presented.
[0084] To disclose the switching function mentioned above, FIG. 10 is presented to point out prominent characteristics of the cross-coupling path 202 that is followed by an unmodulated optical signal through the optical switch 10. In FIG. 10, these characteristics are shown in the context of a cross-coupling length (L.sub.c) cycle of the optical signal. As shown, the cycle begins at a start point 204 and continues to an end point 206. At the end point 206 the optical signal changes direction to start the next cycle. Note that in each cycle the optical signal will pass through the cross-coupling material 100 (see FIG. 11A), and for each cycle the path 202 will have an unmodulated cross-coupling length L.sub.c.
[0085] Still referring to FIG. 10, it is to be appreciated that under the influence of a switching voltage V.sub.π the optical signal will be modulated to follow a modulated optical path 208 (see also FIG. 11B). For purposes of comparison, the modulated optical path 208 is shown in FIG. 10 to begin at the same start point 204, but it will have a different end point 210. Specifically, the difference between end point 206 of the unmodulated path 202 and the end point 210 of the modulated path 208 is an incremental change Δ that is caused by the switching voltage V.sub.π. As envisioned for the present invention, V.sub.π can be measured from a zero voltage or from a V.sub.base. In the latter case, V.sub.base can be established to compensate for fabrication and operational variations. The consequence here is that the unmodulated cross-coupling length L.sub.c on path 202 changes to a modulated cross-coupling length L.sub.c′ on path 208. It is important here to note that, depending on the direction of the electric field E, the incremental change Δ shown in FIG. 10 may be either ±. Accordingly, L.sub.c=L.sub.c′±Δ.
[0086] An important feature of the present invention is that as a modulated optical signal switches back and forth through the cross-coupling material 100 on path 208, the incremental changes Δ are cumulative. Thus, it will happen after switching occurs through an N number of cross-coupling lengths, i.e. an N number of cycles, the optical signal will have traveled along a length L of the cross-coupling material 100, and NΔ will equal L.sub.c′. Thus, the modulated cross-coupling length L.sub.c′=NΔ and L=NL.sub.c=(N±1)L.sub.c′. Furthermore, as an approximation L.sub.c=L.sub.c′, and in reality L.sub.c and L.sub.c′>>Δ.
[0087] Another important feature of the present invention, as shown in FIG. 12, is that the slot 92 between the waveguide-electrodes 34 and 36 will have a separation distance x.sub.c that establishes a confinement factor Γ for the cross-coupling material 100. Specifically, the confinement factor Γ, which is a measure of the optical signal intensity confined in the slot when passing through the cross-coupling material 100, will preferably be greater than 0.15 when x.sub.c is less than 0.35 μm. Preferably, x.sub.c will be less than 0.35 μm and remain essentially within a range between 0.4 μm and 0.04 μm along the common length L of the slot between the waveguide-electrodes. The purpose here is to create a modulated cross-coupling length L.sub.c′ that is less than approximately 2λ under the influence of V.sub.π (i.e. Γ>0.15, when x.sub.c<0.35 μm, to achieve L.sub.c′<2λ).
[0088] With the above in mind, the length L of the cross-coupling material 100 (i.e. the length of slot 92) is established such that the path 202 of the optical signal entering the optical switch 10 will be changed (shorter or longer), during its transit on the path 208 along the length L, by a length that is less than 2λ. After the optical signal has traveled the length L between the waveguide-electrodes 34, 36, the present invention recognizes that the waveguide-electrodes 34, 36 can be separated from each other, and the optical signal will be effectively switched from one waveguide-electrode 34, 36 to the other. As disclosed above, from a structural perspective it is to be appreciated that the width x.sub.c of the slot 92 may vary slightly along the common length L between the waveguide-electrodes 34 and 36. It is also to be appreciated that the orientation between the waveguide-electrodes 34 and 36 may not be absolutely parallel with each other. Indeed, it may be desirable to have a slight divergence between the waveguide-electrodes 34 and 36 at the end of the common length L where the optical signal is switched from one waveguide-electrode (34 or 36) to the other waveguide-electrode (36 or 34).
[0089] While the particular Optical Modulator as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.
